Alternator

ABSTRACT

An alternator exhibits uniform temperature distribution in a rectifier, thereby preventing a locally hot spot from being developed. Positive-side diodes and negative-side diodes are arranged in a zigzag pattern in a circumferential direction, and formed of diodes on an inside diameter side and diodes on an outside diameter side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an alternator equipped with a rectifierfor rectifying alternating current generated at a stator coil intodirect current.

2. Description of the Related Art

FIG. 10 is a sectional view of a conventional automotive alternator,FIG. 11 is an electrical circuit diagram of the alternator, FIG. 12 is afront view of a rectifier 12 of FIG. 10 when the rectifier 12 isobserved from inside, and FIG. 13 is a front view of a rear bracket 2 ofFIG. 10.

The automotive alternator includes: a case 3 composed of an aluminumfront bracket 1 and an aluminum rear bracket 2; a shaft 6 rotatablydisposed in the case 3 and which has a pulley 4 secured to one endthereof; a Lundell-type rotor 7 secured to the shaft 6; a stator 8secured to an inner wall of the case 3; a slip ring 9 secured to theother end of the shaft 6 and which supplies electric current to therotor 7; a pair of brushes 10 that slide in contact with the slip ring9; a brush holder 11 accommodating the brushes 10; a rectifier 12electrically connected to the stator 8 and which rectifies alternatingcurrent generated in the stator 8 into direct current; a heat sink 17fitted in the brush holder 11; and a regulator 18 adhesively fastened tothe heat sink 17 and which adjusts an alternating voltage generated inthe stator 8.

The rotor 7 is equipped with a rotor coil 13 for generating magneticflux on passage of electric current, and a pole core 14 covering therotor coil 13 in which magnetic poles are produced by the magnetic flux.The pole core 14 has a pair of a first pole core assembly 21 and asecond pole core assembly 22 that intermesh with each other. Centrifugalfans 5 for cooling are welded on axial end surfaces of the first polecore assembly 21 and the second pole core assembly 22.

The stator 8 is provided with a stator core 15 through which a rotatingmagnetic field generated by the rotor 7 passes, and a stator coil 16 inwhich alternating current is generated by the rotating magnetic field.The stator coil 16 is constructed by a first stator coil section 16 aand a second stator coil section 16 b, each being formed of three coilswhose conductors are wound around the stator core 15 and which are inY-connection.

FIG. 14 is a front view of the rectifier 12, and FIGS. 15 and 16 areexploded front views of the rectifier 12 of FIG. 14. The rectifier 12includes positive-side diodes 26 and negative-side diodes 28 connectedto output ends of the first stator coil section 16 a and the secondstator coil section 16 b, and neutral point diodes 30 connected toneutral points 31 of the first stator coil section 16 a and the secondstator coil section 16 b.

The rectifier 12 further includes: a circular strip-shaped positive-sideheat sink 24 having, on its surface, six positive-side diodes 26 and twoneutral point diodes 30 equidistantly provided on the samecircumference; a circular strip-shaped negative-side heat sink 27disposed radially outside of and on the same plane as the positive-sidediodes 26, and has, on its surface, six negative-side diodes 28 and twoneutral point diodes 30 equidistantly provided on the samecircumference; and a circuit board 29 electrically connecting the diodes26, 28, and 30, and the stator coil 16.

The surfaces of the positive-side heat sink 24 and the negative-sideheat sink 27 have recesses 32 and 33 for accommodating the columnarpositive-side diodes 26, the negative-side diodes 28, and the neutralpoint diodes 30. FIG. 17 shows the positive-side heat sink 24 and thenegative-side heat sink 27 of the FIG. 15 as observed from a rear side.On the rear surfaces of the heat sinks 24 and 27, protuberances 34 and35 are formed at the same time when the recesses 32 and 33 are formed.

The positive-side diodes 26, the negative-side diodes 28, and theneutral point diodes 30 are fixed to the recesses 32 and 33 of the heatsinks 24 and 27 by soldering. Perpendicularly extending lead wires 36and 37 of the diodes 26, 28, and 30 are electrically connected toterminals 38 and 39 of the circuit board 29.

The positve-side heat sink 24 is retained on the negative-side heat sink27 via a holder 40. The positive-side heat sink 24, the negative-sideheat sink 27, and the circuit board 29 are fixed in the case 3 by screws(not shown) attached to the rear bracket 2 via through holes 41.Furthermore, the negative-side heat sink 27 is grounded by beingdirectly attached to the rear bracket 2.

In the automotive alternator having the construction set forth above,electric current is supplied from a battery (not shown) to the rotorcoil 13 via the brushes 10 and the slip ring 9, generating magneticflux. The pulley 4 is driven by an engine, and the rotor 7 is rotated bythe shaft 6. This causes a rotating magnetic field to be imparted to thestator coil 16, so that an electromotive force is generated in thestator coil 16. The alternating electromotive force is converted intodirect current through the positive-side diodes 26 and the negative-sidediodes 28 of the rectifier 12, a magnitude thereof is adjusted by theregulator 18, and the battery is recharged.

The rotor coil 13, the stator coil 16, the positive-side diodes 26, thenegative-side diodes 28, and the regulator 18 constantly generate heatduring power generation. When an alternator of, for example, a 100Arated output current class, runs at a speed generating a hightemperature, the rotor coil 13 generates a calorific value of 60W, thestator coil 16 generates a caloric value of 500W, the positive-sidediodes 26 and the negative-side diodes 28 together generate a calorificvalue of 120W, and the regulator 18 generates a calorific value of 6W.Excessive heat generation causes deteriorated performance of thealternator and shortens lives of components.

As countermeasures for the heat generation, the fans 5 rotate as therotor 7 rotates. The rotation of the fans 5 causes outside air to beintroduced into the case 3 through an aperture A of the case 3, and toflow as indicated by arrows a of FIG. 10 to thereby cool thenegative-side heat sink 26, the negative-side diodes 28, thepositive-side heat sink 24, and the positive-side diodes 26. The outsideair is then led radially outward by the fans 5 to cool a coil end of thestator coil 16 at the rear side, and exhausted to open air through anaperture B.

Furthermore, the rotation of the fans 5 causes outside air to beintroduced into the case 3 also through an aperture C. The outside airflows as indicated by arrows β of FIG. 10 to cool a power transistor ofthe regulator 18. The outside air is then led radially outward by thefans 5 to cool a coil end of the stator coil 16 at the rear side, andexhausted to open air through an aperture D.

Similarly, outside air introduced through apertures E of the frontbracket 1 is directed radially outward by the fans 5 to cool an end ofthe stator coil 16 at a front side. The outside air is then exhaustedout of the case 3 through an aperture F.

In the automotive alternator having the construction described above,the lead wires 36 and 37 of the positive-side diodes 26 and thenegative-side diodes 28, which extend in an axial direction of the shaft6, are directly abutted against the terminals 38 and 39 of the circuitboard 29. For this reason, the six positive-side diodes 26 and the twoneutral point diodes 30 are disposed at equal intervals on thecircumference of the positive-side heat sink 24, and the sixnegative-side diodes 28 and the two neutral point diodes 30 are disposedat equal intervals on the circumference of the negative-side heat sink27. Therefore, the positive-side diodes 26, in particular, on thepositive-side heat sink 24 on an inside diameter side are close to eachother. When a distance between central points of the positive-sidediodes 26 is denoted as W, and a diameter of the positive-side diodes 26is denoted as D, a value expressed as W/D≅1.5 is obtained. A study oftemperature distribution of the rectifier 12 has revealed that thetemperature rises toward a center in a circumferential direction of thepositive-side heat sink 24, a difference between temperature extremesbeing approximately 13 degrees Celsius, while the temperature risesinward in a radial direction, a difference between temperature extremesbeing approximately 3 degrees Celsius. There has been a problem in thatthe positive-side diode 26 at the center of the positive-side heat sink24 where the temperature is the highest reaches a locally hightemperature, 125 degrees Celsius.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made with a view towardsolving the problems described above, and it is an object thereof toprovide an alternator that exhibits uniform temperature distribution ina rectifier, thereby preventing a locally hot place from beingdeveloped.

To this end, according to one aspect of the present invention, there isprovided an alternator having at least a first diode assembly or asecond diode assembly composed of diodes on an inside diameter side anddiodes on an outside diameter side arranged in a zigzag pattern in acircumferential direction.

In a preferred form of the alternator in accordance with the presentinvention, the diodes on the inside diameter side and the diodes on theoutside diameter side are provided in recessions of a heat sink having arecessed surface, and protuberances associated with the recesses areformed in a rear surface of the heat sink.

In a preferred form of the alternator in accordance with the presentinvention, one of the diode on the inside diameter side and the diode onthe outside diameter side is disposed such that it is partly included ina region of an air detachment portion produced on a peripheral surfaceby cooling air that collides with the other of the diode on the insidediameter side and the diode on the outside diameter side.

In another preferred form of the alternator in accordance with thepresent invention, if a distance between a central point of a columnardiode on the inside diameter side and a central point of its adjacentcolumnar diode on the outside diameter side is denoted as W, and adiameter of the diode on the inside diameter side and the diode on theoutside diameter side is denoted as D, then (W/D)<2. Furthermore, if anangle at which a line connecting a central point of the diode on theinside diameter side and a central point of its adjacent diode on theoutside diameter side crosses a line connecting a central axis of ashaft and the central point of the diode on the outside diameter side orthe diode on the inside diameter side is denoted as θ, then angle θ is100°<θ<140°.

In a preferred form of the alternator according to the presentinvention, diodes on the outside diameter side that are secured to thesecond heat sink are disposed so as to oppose the diodes on the outsidediameter side that are secured to the first heat sink.

In a preferred form of the alternator according to the presentinvention, the diodes on the outside diameter side and the diodes on theinside diameter side that are secured to the second heat sink aredisposed away from radial lines of the diodes on the outside diameterside and the diodes on the inside diameter side that are secured to thefirst heat sink.

In a preferred form of the alternator according to the presentinvention, the first heat sink and the second heat sink are disposed ondifferent vertical planes with respect to axes.

In a preferred form of the alternator according to the presentinvention, the first heat sink is a positive-side heat sink, the firstdiode assembly is a positive-side diode assembly, the second heat sinkabutted against the case is a negative-side heat sink, and the seconddiode assembly is a negative-side diode assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a rectifier of an automotive alternatoraccording to a first embodiment of the present invention.

FIG. 2 is a front view of the rectifier shown in FIG. 1, from which acircuit board has been removed.

FIG. 3 is a rear view of the rectifier shown in FIG. 2.

FIG. 4 is an enlarged view of an essential section of the rectifiershown in FIG. 2.

FIG. 5 is a chart showing a local Nusselt number Nux of a column placedat right angles to a flow.

FIG. 6 is a front view of a rectifier of an automotive alternatoraccording to a second embodiment of the present invention.

FIG. 7 is a front view of a rectifier of an automotive alternatoraccording to a third embodiment of the present invention.

FIG. 8 is a front view of a rectifier of an automotive alternatoraccording to a fourth embodiment of the present invention.

FIG. 9 is a sectional view of an automotive alternator according to asixth embodiment of the present invention.

FIG. 10 is a sectional side elevation of a conventional automotivealternator.

FIG. 11 is an electrical circuit diagram of the automotive alternator ofFIG. 10.

FIG. 12 is a front view of a rectifier of the automotive alternatorshown in FIG. 10, as observed from inside thereof.

FIG. 13 is a front view of a rear bracket of the automotive alternatorshown in FIG. 10.

FIG. 14 is a front view of the rectifier shown in FIG. 10.

FIG. 15 is a front view of the rectifier shown in FIG. 10, from which acircuit board has been removed.

FIG. 16 is a front view of the circuit board shown in FIG. 14.

FIG. 17 is a rear view of the rectifier shown in FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An automotive alternator according to a first embodiment of the presentinvention will be described. Components that are the same as orequivalent to those shown in FIG. 10 through FIG. 17 will be assignedthe same reference numerals in the descriptions.

First Embodiment

FIG. 1 is a front view of a rectifier 50 of an automotive alternatoraccording to the first embodiment of the present invention, and FIG. 2is a front view of the rectifier 50, from which a circuit board 56 shownin FIG. 1 has been removed.

The rectifier 50 includes: positive-side diodes 51 a and 51 b, which arefirst diodes, and negative-side diodes 52 a and 52 b, which are seconddiodes, the first and second diodes being connected to output ends of afirst stator coil section 16 a and a second stator coil section 16 b,respectively; and neutral point diodes 53 connected to neutral points 31of the first stator coil section 16 a and the second stator coil section16 b.

The rectifier 50 further includes: a circular strip-shaped positive-sideheat sink 54 which is a first heat sink and has, on its surface, sixpositive-side diodes 51 a and 51 b and two neutral point diodes 53; acircular strip-shaped negative-side heat sink 55, which is a second heatsink, disposed a radially outside of and on the same plane as thepositive-side heat sink 54, and has, on its surface, six negative-sidediodes 52 a and 52 b, and two neutral point diodes 53; and a circuitboard 56 electrically connecting the diodes 51 a, 51 b, 52 a, 52 b, and53, and a stator coil 16.

The surfaces of the positive-side heat sink 54 and the negative-sideheat sink 55 have recesses 57 and 58 formed to accommodate the columnarpositive-side diodes 51 a and 51 b (the diodes 51 a are located on aninside diameter side, while the diodes 51 b are located on an outsidediameter side), the negative-side diodes 52 a and 52 b (the diodes 52 aare located on the inside diameter side, while the diodes 52 b arelocated on the outside diameter side), and the neutral point diodes 53.FIG. 3 shows the positive-side heat sink 54 and the negative-side heatsink 55 of the FIG. 2, as observed from a rear side. On the rearsurfaces of the heat sinks 54 and 55, protuberances 59 and 60 are formedat the same time when the recesses 57 and 58 are formed.

The positive-side diodes 51 a and 51 b, the negative-side diodes 52 aand 52 b, and the neutral point diodes 53 are fixed to the recesses 57and 58 of the heat sinks 54 and 55 by soldering. Lead wires 61, 62, and63 of the diodes 51 a, 51 b, 52 a, 52 b, and 53 are electricallyconnected to terminals 64 and 65 of the circuit board 56.

Positive-side diodes 51 a and 51 b on the positive-side heat sink 54 arealternately arranged on the inside diameter side and the outsidediameter side of the positive-side heat sink 54 in a zigzag pattern in acircumferential direction. Similarly, negative-side diodes 52 a and 52 bon the negative-side heat sink 55 are alternately arranged on the insidediameter side and the outside diameter side of the negative-side heatsink 55 in a zigzag pattern in a circumferential direction. Hence, adistance L1 between the positive-side diode 51 a and the negative-sidediode 52 b that are radially adjacent is different in thecircumferential direction from a distance L2 between the positive-sidediode 51 b and the negative-side diode 52 a that are radially adjacent.Therefore, when electrically connecting the lead wires 61, 62, and 63 ofthe diodes 51 a, 51 b, 52 a, 52 b, and 53 to the terminals 64 and 65 ofthe circuit board 56, the lead wires 61, 62, and 63 are bent in themiddle thereof for the greater distance L2.

The positive-side heat sink 54 is retained on the negative-side heatsink 55 via a holder 40. The positive-side heat sink 54, thenegative-side heat sink 55, and the circuit board 56 are fixed in a case3 by screws (not shown) attached to a rear bracket 2 via through holes41. Furthermore, the negative-side heat sink 55 is grounded by beingdirectly attached to the rear bracket 2.

In this embodiment, the positive-side diodes 51 a and 51 b are disposedso that, when a distance between central points of the positive-sidediodes 51 a and 51 b is denoted as W, and a diameter of thepositive-side diodes 51 a and 51 b is denoted as D, a value expressed asW/D≅1.5 is obtained, and an angle at which a line 100 connecting acenter point of the diode 51 b on the outside diameter side (hereinafterreferred to simply as “the outer diode 51 b”) on the positive-side heatsink 54 and a center point of the rectifier 50 intersects with a line101 connecting the center point of the outer diode 51 b and a centerpoint of the diode 51 a on the inside diameter side (hereinafterrefereed to simply as “the inner diameter 51 a”) adjacent to the diode51 b is 112.5 degrees.

A study of temperature distribution of the rectifier 50 under the sameconditions as those of a conventional rectifier has revealed that thetemperature rises toward a center in a circumferential direction, adifference between temperature extremes being approximately 10 degreesCelsius, meaning a temperature drop of 5 degrees Celsius. Furthermore,the temperature rises inward in a radial direction, a difference betweentemperature extremes being approximately 1 degree Celsius, meaning atemperature drop of 2 degrees Celsius. Temperatures of the positive-sidediodes 51 a and 51 b at a central portion of the positive-side heat sink54, which are the highest temperatures, are 120 degrees Celsius, whichindicates a temperature drop of 5 degrees Celsius.

Thus, the temperature distribution of the rectifier 50 has become even,and the maximum temperature of the positive-side diodes 51 a and 51 bhas dropped. The improved cooling efficiency is considered to be due tothe following reason.

FIG. 4 is a partial enlarged view of the positive-side heat sink 54,which is the first heat sink, and shows a flow of air that collidesagainst the columnar outer diode 51 b on the positive-side heat sink 54and moves along side surfaces thereof. When the air collides against thediode 51 b, it branches onto the two sides thereof, and the flow isblocked at a branching point, resulting in zero velocity. Behind thatpoint, namely, a stagnation point 200, a laminar boundary layer isformed along the side surfaces, then the branched flow is detached fromthe side surfaces. At the rear, a detached air portion 201 wherein avortex or backflow is generated is formed. The inner diodes 51 a aredisposed most closely to the detached air portion 201. Thus, it isconsidered that the inner diodes 51 a are partly involved in thedetached air portion 201, which is a turbulent area, leading to promotedheat transfer on peripheral wall surfaces of the inner diodes 51 a.

FIG. 5 shows local Nusselt number Nux of a column placed at right anglesto a flow (αxD/λ, where αx denotes a local heat transfer coefficient onthe column, D denotes a diameter of the column, and λ denotes thermalconductivity of a fluid. The values of diameter D and thermalconductivity λ are fixed, so that a larger value of Nux means betterlocal heat transfer). This information is provided on page 168 of“Thermal Conductology” published by Rikogaku. In the chart, the axis ofabscissa indicates an angle θ (the angle θ is 180 degrees at a positionopposing the stagnation point) from the stagnation point 200 to apredetermined position on a side surface of the column, the stagnationpoint 200 being zero, and the axis of ordinates indicates the Nusseltnumber at the predetermined position. As can be understood from thechart, the Nusselt number shows larger values when the angle θ is in arange of 100 to 140 degrees. In other words, it is considered that theNusselt number shows especially larger values due to the generateddetached air portion 201.

Accordingly, setting the angle θ to the range of 100 to 140 degrees inFIG. 4 causes an air layer of the peripheral wall surfaces of theadjoining inner diodes 51 a to be disturbed due to influences exerted bythe detached air portion 201 produced by the outer diode 51 b. Thispermits the positive-side diode 51 b to be efficiently cooled.

In order to cause the adjoining inner diodes 51 a to be influenced bythe detached air portion 201, the outer diode 51 b must be close to theinner diodes 51 a to a certain extent. Influences exerted by a flowaround the column have been disclosed by many examples of experimentscarried out in the past. Results of such experiments have revealed thatthe influences are exerted on adjoining columns when (W/D)<2 (refer to,for example, VIII-INTERFERENCE DRAG 8-2).

Thus, in the automotive alternator according to the first embodiment setforth above, the inner diodes 51 a and the outer diodes 51 b on thepositive-side heat sink 54 are arranged in the zigzag pattern in thecircumferential direction, and the inner diodes 51 a are subjected tothe influences of the detached air portion 201 generated at the outerdiode 51 b. This arrangement ensures efficient cooling of the innerdiodes 51 a. Similarly, the protuberances 59 on the rear side of thepositive-side heat sink 54 produces the detached air portion, and theheat transfer of the protuberance 59 adjacent to the detached airportion is promoted, also causing the rear side of the positive-sideheat sink 54 to be efficiently cooled.

In addition, the negative-side diodes 52 a and the negative-side diodes52 b on the negative-side heat sink 55, which is the second heat sink,are also arranged in the zigzag pattern in the circumferentialdirection. Hence, a distance between adjoining negative-side diodes 52 aand 52 b is greater than it would if they were arranged on the samecircumference, resulting in a reduced ventilation drag. This leads toincreased ventilation with consequent higher efficiency of cooling theentire rectifier 50.

Second Embodiment

FIG. 6 is a front view of a rectifier 70 of an automotive alternatoraccording to a second embodiment of the present invention, a circuitboard thereof having been removed. The construction of the secondembodiment is the same as that of the first embodiment except that alayout of negative-side diodes 71 a and 71 b, which are second diodes,is different.

The second embodiment is adapted to enhance influences of a detachedportion 201 from an outer diode 51 b 1 adjacent to an inner diode 51 a 1(a central portion of the positive-side heat sink 54, which is a firstheat sink) where temperature is the highest. More specifically, in orderto increase a volume of air colliding with the outer diode 51 b 1adjacent to the inner diode 51 a 1 at the central portion, a distance Lbetween the outer diode 51 b 1 and an outer diode 71 b 1 radiallylocated on an outer side is increased by disposing the outer diode 71 b1 on an outer diameter side of a negative-side heat sink 55, which is asecond heat sink.

Third Embodiment

FIG. 7 is a front view of a rectifier 90 of an automotive alternatoraccording to a third embodiment of the present invention, a circuitboard thereof having been removed therefrom. The construction of thethird embodiment is the same as that of the second embodiment exceptthat a layout of negative-side diodes 91 a and 91 b, which are seconddiodes, is different.

In the third embodiment, the outer diodes 91 b and the inner diodes 91 aare disposed away from a radial line G of outer diodes 51 b and innerdiodes 51 a secured to a positive-side heat sink 54, which is a firstheat sink. This arrangement increases a volume of cooling air that flowsinward in a radial direction and collides with the outer diodes 51 b andthe inner diodes 51 a secured to the positive-side heat sink 54, thusfurther efficiently cooling the outer diodes 51 b and the inner diodes51 a.

Fourth Embodiment

FIG. 8 is a sectional view of an automotive alternator according to afourth embodiment of the present invention. The construction of thefourth embodiment is the same as that of the first embodiment exceptthat a positive-side heat sink 81 and a negative-side heat sink 82 aredisposed on different vertical planes with respect to an axis of a shaft6.

In this embodiment, the positive-side heat sink and the negative-sideheat sink are not on the same plane, so that ventilation drag on theplanes is reduced, and a volume of air introduced through an aperture Ais increased. This makes it possible to suppress a rise in temperatureof positive-side diodes 51 and negative-side diodes 52.

Fifth Embodiment

In the embodiments described above, the columnar diodes project from thefront surfaces of the heat sinks, and protuberances are formed on therear surfaces to promote heat transfer by disturbance in the detachedair portions on both surfaces. Alternatively, however, the inner diodesand the outer diodes may be accommodated in the recesses of the heatsinks so that the front surfaces of the diodes are flush with the frontsurfaces of the heat sinks.

More specifically, the protuberances jutting out of the rear surfaces ofthe heat sinks associated with the recesses housing the inner diodes maybe disposed so that they are partly included in the areas of thedetached air portion produced by collision against the protuberancesjutting out of the rear surfaces of the heat sinks associated with therecesses housing the outer diodes. In this case, the heat transferpromotion effect from the disturbance in the detached air portion isobtained at the rear surfaces of the heat sinks.

Sixth Embodiment

FIG. 9 is a sectional view of an automotive alternator according to asixth embodiment of the present invention.

In the above embodiments, the rectifier 50, 70, or 90 is housed in thecase 3, while in the sixth embodiment, a rectifier 100 is housed in acover 102 adjacent to a rear bracket 101. As in the case of the firstembodiment, the rectifier 100 has inner and outer positive-side diodes103 arranged in a zigzag pattern in a circumferential direction, andinner and outer negative-side diodes 104 arranged in the zigzag patternin the circumferential direction. The inner positive-side diodes 103 aredisposed so that they are partly included in an area of a detached airportion generated on a circumferential surface by cooling air thatcollides against the outer positive-side diodes 103. A positive-sideheat sink 105 and a negative-side heat sink 106 are disposed on verticalplanes that are different with respect to axes.

In the sixth embodiment, the inner positive-side diodes 103 aresubjected to the influences of a detached air portion generated at theouter positive-side diodes 103, so that the inner positive-side diodes103 are efficiently cooled, as in the case of the first embodiment.Furthermore, the negative-side heat sink 106 and the positive-side heatsink 105 are not on the same plane, so that ventilation drag on theplanes is reduced, and a volume of air introduced through an aperture Hof the cover 102 is increased. This makes it possible to suppress a risein temperature of the positive-side diodes 103 and the negative-sidediodes 104.

In the above embodiments, the negative-side heat sink is disposed on theoutside diameter side, and the positive-side heat sink is disposed onthe inside diameter side. Obviously, however, the present invention canbe applied to a rectifier wherein the negative-side heat sink isdisposed on the inside diameter side, and the positive-side heat sink isdisposed on the outside diameter side.

The rectifier in each of the above embodiments is equipped with neutralpoint diodes connected to the neutral points, and four diodes aredisposed in each heat sink. Alternatively, however, only three diodesper heat sink, which is a number of diodes required for three-phasefull-wave rectification, may be used. Obviously, the present inventionis also applicable to a case wherein a number of diodes disposed on theouter heat sink is greater than a number of diodes disposed on the innerheat sink.

Furthermore, only the positive-side diodes or the negative-side diodesmay be arranged in the zigzag pattern in the circumferential direction.

The shape of the positive-side diodes and the negative-side diodes isnot limited to the columnar shape; it may alternatively be a rectangularor polygonal shape.

In the above embodiments, the positive-side diodes are disposed so thatonly the inner positive-side diodes are disposed to be partly includedin the area of the detached air portion. Alternatively, however, thenegative-side diodes may be disposed so that the outer negative-sidediodes are partly included in the area of the detached air portion.

Furthermore, in the above embodiments, the descriptions have been givenof a case wherein the cooling air flows inward in the radial direction.The present invention, however, may also be applied to a case whereinthe cooling air flows in the vicinity of the shaft into the case andmoves outward in the radial direction. In this case, therefore, theouter diodes are efficiently cooled by the heat transfer promotioneffect by the disturbance in the detached air portion caused by theinner diodes.

It is also obvious that the application of the present invention is notlimited to an automotive alternator.

As described above, the present invention provides the followingadvantages.

As described above, in an alternator according to one aspect of thepresent invention, at least either the first diodes or the second diodesis composed of diodes on an inside diameter side and diodes on anoutside diameter side that are arranged in a zigzag pattern in acircumferential direction. Therefore, the drag of the cooling airflowing into the rectifier is reduced, so that a cooling flow isincreased, resulting in higher cooling efficiency of the rectifier.There is another advantage in that the rectifier can be made compact,and a degree of freedom for disposing the diodes is increased.

According to another form of the alternator, the diodes on the insidediameter side and the diodes on the outside diameter side may beprovided in recessions of a heat sink having a recessed surface, andprotuberances associated with the recesses may be formed in a rearsurface of the heat sink. Therefore, An area of contact between the heatsinks and the cooling air is increased, leading to higher coolingefficiency of the diodes.

According to still another form of the alternator, one of the diode onthe inside diameter side and the diode on the outside diameter side maybe disposed such that it is partly included in a region of an airdetachment portion produced on a peripheral surface by cooling air thatcollides with the other of the diode on the inside diameter side and thediode on the outside diameter side. Therefore, One of the inner diode orthe outer diode is efficiently cooled by the heat transfer promotioneffect by the disturbance in the detached air portion that takes placein the other of the inner diode or the outer diode.

According to still another form of the alternator, if a distance betweena central point of a columnar diode on the inside diameter side and acentral point of its adjacent columnar diode on the outside diameterside is denoted as W, and a diameter of the diode on the inside diameterside and the diode on the outside diameter side is denoted as D, then(W/D)<2, and if an angle at which a line connecting a central point ofthe diode on the inside diameter side and a central point of itsadjacent diode on the outside diameter side crosses a line connecting acentral axis of a shaft and the central point of the diode on theoutside diameter side or the diode on the inside diameter side isdenoted as H, then angle θ is 100°<θ<140°. Therefore, one of the innerdiode or the outer diode is efficiently cooled by securely benefitingfrom the heat transfer promotion effect by the disturbance in thedetached air portion that takes place in the other of the inner diode orthe outer diode.

According to still another form of the alternator, the diodes on theoutside diameter side that are secured to the second heat sink may bedisposed so as to oppose the diodes on the outside diameter side thatare secured to the first heat sink. Therefore, A space between opposingdiodes can be securely provided, making it possible to reduce theventilation drag and increase the volume of air that collides againstthe outer diodes or the inner diodes.

According to still another form of the alternator, the diodes on theoutside diameter side and the diodes on the inside diameter side thatare secured to the second heat sink may be disposed away from radiallines of the diodes on the outside diameter side and the diodes on theinside diameter side that are secured to the first heat sink. Therefore,the volume of cooling air that collides against the diodes increases,permitting the diodes to be cooled further efficiently.

According to still another form of the alternator, the first heat sinkand the second heat sink may be disposed on different vertical planeswith respect to an axis. Therefore, The ventilation drag on the sameplane is reduced, permitting the first diodes and the second diodes tobe cooled further efficiently.

According to still another form of the alternator, the first heat sinkmay be a positive-side heat sink, the first diodes may be positive-sidediodes, the second heat sink abutted against the case may be anegative-side heat sink, and the second diodes may be negative-sidediodes. Therefore, the heat of the negative-side diodes is transmittedto the case due to heat conduction, permitting the negative-side diodesto be cooled further efficiently.

What is claimed is:
 1. An alternator comprising: a case; a shaft rotatably provided in said case; a rotor secured to said shaft; a stator secured to said case and provided with a stator coil composed of a stator core around which a lead wire is wound; and a rectifier electrically connected to said stator coil and which rectifies an alternating current, which is generated in said stator coil, into direct current, wherein said rectifier comprises: a first circular strip-shaped heat sink which is orthogonalized with said shaft and has a plurality of first diodes secured thereto; and a second circular strip-shaped heat sink which is provided outside said first heat sink so that it is orthogonalized with said shaft, and has a plurality of second diodes secured thereto; at least one of said first diodes or said second diodes being composed of diodes on an inside diameter side and diodes on an outside diameter side that are arranged in a zigzag pattern in a circumferential direction, wherein a distance W between a central point of a columnar diode on the inside diameter side and a central point of its adjacent columnar diode on the outside diameter side and a diameter D of said diode on the inside diameter side and said diode on the outside diameter side satisfy the equation (W/D)<2, and an angle θ formed between a line connecting a central point of said diode on the inside diameter side and a central point of its adjacent diode on the outside diameter side and a line connecting a central axis of said shaft and the central point of said diode on the outside diameter side or said diode on the inside diameter side satisfies the equation 100°<θ<140°.
 2. An alternator according to claim 1, wherein said diodes on the inside diameter side and said diodes on the outside diameter side are provided in recessions of said first and second circular strip-shaped heat sinks having a recessed surface, and protuberances associated with said recesses are formed in a rear surface of said first and second circular strip-shaped heat sinks.
 3. An alternator according to claim 1, wherein one of said diodes on the inside diameter side and said diodes on the outside diameter side are disposed such that they are partly included in a region of an air detachment portion produced on a peripheral surface by cooling air that collides with the other of said diodes on the inside diameter side and said diodes on the outside diameter side.
 4. An alternator according to claim 1, wherein said diodes on the outside diameter side that are secured to said second heat sink are disposed so as to oppose said diodes on the outside diameter side that are secured to said first heat sink.
 5. An alternator according to claim 1, wherein said diodes on the outside diameter side and said diodes on the inside diameter side that are secured to said second heat sink are disposed away from radial lines of said diodes on the outside diameter side and said diodes on the inside diameter side that are secured to said first heat sink.
 6. An alternator according to claim 1, wherein said first heat sink and said second heat sink are disposed on different vertical planes with respect to an axis.
 7. An alternator according to claim 1, wherein said first heat sink is a positive-side heat sink, said first diodes are positive-side diodes, said second heat sink abutted against said case is a negative-side heat sink, and said second diodes are negative-side diodes. 